After some more discussions with one of our mentors, it appears that our use of digital potentiometers for voltage control was ill conceived. Instead, we’re much better off with digital-to-analog converters, which will give us 16-bit resolution, while the digital potentiometers were limited to 8-bit. If we decide to stick with Analog Devices, the best option seems to be the AD5360, which would give us 16 channels and a nice SPI interface. At $30 a piece, they’re a bit expensive, but we just need one of them per channel.
With such a modification, we are replacing 4 quad-channel potentiometers by a single DAC component, which will save us some real estate on the backplane. In order to further simplify our design, I’ve decided to remove the PLCC sockets for the AD75019 crosspoint switches, and have the two of them directly soldered on the board. This means that our backplane won’t be extensible from 16 to 32 crosspoint bus endpoints, and will offer all 32 endpoints by default. This brings our BoM to just over $800, which remains within the bounds that we had originall set.
As a result, we just have 4 major components per channel on our backplane, leaving plenty of room for many other things that will be discussed in further posts.